Polyphenylene ether resins comprise a class of thermoplastics which are characterized by outstanding physical properties, including hydrolytic stability, excellent dielectric properties, broad temperature use range and dimensional stability at elevated temperatures. They can be made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. In general, they are prepared by the oxidative coupling of a phenolic compound with a complex copper catalyst. By way of illustration, descriptions of the preparation of polyphenylene ether resins are contained in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358, which are incorporated herein by reference.
In the Hay patents, the polyphenylene ether resins are prepared by oxidative coupling comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. In the Stamatoff patents, the polyphenylene ethers are prepared by reacting the corresponding phenolate ion with an initiator, e.g., an acid peroxide, in the presence of a complexing agent.
Disclosures relating to the preparation of polyphenylene ether resins using metal catalysts which do not include amines are found in Wieden et al, U.S. Pat. No. 3,442,885 (copper-amidines), Nakashio et al, U.S. Pat. No. 3,573,257 (metal-alcoholates or metal phenolates), and Kobayashi et al, U.S. Pat. No. 3,455,880 (cobalt chelates). The preparation of polyphenylene ethers by a non-catalytic process, e.g., oxidation with lead dioxide, silver oxide, and the like, is described in Price et al, U.S. Pat. No. 3,382,212. The disclosures of all of these references are incorporated herein by reference, to save unnecessary detail.
The processing of polyphenylene ether resins on injection molding and extrusion equipment is enhanced when the polyphenylene ethers are combined with styrene resins, e.g., crystal homopolystyrene or rubber-modified high-impact polystyrenes. These polymers are combinable in a wide range of proportions, e.g., from 1 to 99 parts of polyphenylene ether and from 99 to 1 parts of styrene resin. Compositions comprising from 10 to 60 parts of polyphenylene ether and 90 to 40 parts of styrene resin offer an especially wide range of desirable design properties. Such combinations are disclosed in Cizek, U.S. Pat. No. 3,383,435, which is incorporated herein by reference.
Although polyphenylene ethers are normally self-extinguishing, the addition of styrene resin leads to molding compositions and molded articles which are normally flammable, i.e., they have poor flame retardant properties and are thus unable to meet the minimum requirements established by various testing groups, such as Underwriters' Laboratories. Moreover, the compositions drip flaming resin while burning, which is a serious shortcoming and is not permitted by more stringent tests.
Flame retardant, or self-extinguishing, polyphenylene ether resin compositions are known in the art. These generally involve the addition of flame retardant agents such as halogenated organic compounds, phosphorus compounds, antimony compounds, and the like. These approaches are not completely satisfactory, however, because when sufficient flame retardant is added, physical properties deteriorate. Moreover, the more efficient flame-retardant additives are too expensive.
Recently it has been proposed that normally flammable compositions comprising a polyphenylene ether resin and a styrene resin can be rendered self-extinguishing, with less tendency to give off smoke, by the addition of a flame-retardant combination of a halogenated aromatic compound and ferrocene. The resulting flame retardant thermoplastic compositions also possess good impact strength.
It has now been discovered that when a fatty acid terminated saturated polyester is added to thermoplastic compositions comprising a polyphenylene ether resin, a styrene resin, a halogenated aromatic flame retardant agent and ferrocene, the resulting thermoplastic composite is not only self-extinguishing, but is also moldable to articles having improved impact strength. Even more surprisingly, the compositions while molten possess greater thermal resistance, as indicated by undergoing less discoloration upon extrusion, and they have less tendency to drip molten or flaming resin. As a result, the compositions of this invention are more readily processable and are safer to use.